This invention pertains to magnetic head structures and more particularly to magnetic head structures including writing and reading magnetic transducers in close proximity and operating at the same time.
With magnetic head structures where simultaneous reading and writing take place there is always the problem of feedthrough. Feedthrough is the signal measured at the read transducer with the magnetic medium stationary while the winding of the write transducer is fed a normal write current. In many currently available magnetic head structures this feedthrough signal is high enough to make the reliability of reading information signals questionable.
The feedthrough problem has been known for quite some time and many techniques have been developed to reduce its effects. One technique is to provide a conductive layer (copper or silver) over the surface of the writing and reading transducers with openings exposing the reading and writing gaps to allow magnetic medium contact with these. This shielding has a limited effect in that it reduces primarily the high frequency components of the feedthrough signal and does little for the lower frequency components of such signal. Another disadvantage of this technique is the high manufacturing costs associated with the forming or plating a conductive layer, then exposing the working gaps.
Another technique to achieve reduced feedthrough is to supply a shield with a coil wound on it to produce a magnetic field opposing the feedthrough field. This shield is placed between the writing and reading transducers and is oriented transversely to the movement of the magnetic medium (tape, drum, disc, etc). This technique requires a circuit for energizing the coil in response to operation of the writing transducer. This circuit must shape and phase the signal so that particular field is produced in the area of the read transducer gap for opposing and cancelling the feedthrough field. This technique does reduce the feedthrough signal somewhat, but again the costs associated with supplying a field producing shield in the center section and located between the read and write transducers is high. Also, the amount of room (most times under one-tenth of an inch) available in the center section is limited. This compounds the difficulty of supplying a field producing shield in this area. Furthermore, the field producing shield must be mechanically different from the cores of the read and write transducers further adding to the number of different parts required for the structure. This need for the neutralizing element to fit in center section of the structure and because of its mechanical difference from the other transducers, produces a compensating circuit which further adds to the cost and manufacturing problems of the head structure. It has been proposed to use a combination of these two methods and it has been claimed that a reduction of 100 to 1 has been achieved when both these methods are employed. The disadvantages to this approach are the high cost and manufacturing difficulties.
With other feedthrough neutralizing techniques circuits are provided which must be custom "tuned" or adjusted for each head structure.
It accordingly is a general object of the invention to provide an improved head structure.
It is another object of the invention to provide an improved head structure utilizing write and read transducers wherein the feedthrough signals have been reduced by a factor of a thousand.
It is a further object of the invention to provide an improved head structure utilizing write and read transducers wherein the feedthrough signals are reliably neutralized in a simple and inexpensive manner.
It is still a further object of the invention to provide a feedthrough signal neutralized head structure which requires no particular tuning or adjusting.
Briefly, the invention contemplates a magnetic head structure having first and second magnetic transducers each with a core-carrying winding. The magnetic transducers are positioned to cooperate with the same channel of the magnetic medium so that the first of the magnetic transducers is adapted to record signals on the medium while the second is adapted to reproduce the signals recorded by the first magnetic transducer. A neutralizing magnetic transducer having at least a winding is positioned laterally of one of the first and second magnetic transducers with the winding of the neutralizing magnetic transducer in a common circuit, but in phase opposition with the winding of one of the first and second magnetic transducers.